Telescópios: Radiotelescópios

Telescópios:

Radiotelescópios

Prof. Jorge Meléndez

Os principios básicos de radio astronomia foram

apresentados no seminário do Jullian. A seguir informações

complementares sobre o tema.

The radio region

The radio region observable from Earth occupies a wide range within

the electromagnetic spectrum.

The wavelength region in which Earth-based radio astronomy can be pursued comprises wavelengths 15 (or 20) m - 1 mm. This corresponds to frequencies of between (15) 20 MHz and 300 GHz.

H₂O Reflected

or

Porque demorou tanto?

Astrônomos sabiam demais …

Em ondas de rádio:

Replacing

the

exponential term

in

Planck's equation

by its

Taylor-series

approximation

Inicio da radioastronomia

Natural radio emission from our Galaxy was detected accidentally in 1932 by Karl Guthe Jansky, a physicist working as a radio engineer for Bell Telephone Laboratories.

Karl Jansky (1905-1950) and the antenna that discovered cosmic

radio static at 20.5 MHz. It rotated in

azimuth on four wheels scavenged from a Ford Model T. An accurate replica of this antenna is located at the NRAO in Green Bank, WV.

The New York Times of May 5, 1933

''New Radio Waves

Traced to Centre of the

Milky Way.''

Astronomers ignored this

discovery, because they

couldn’t understand how

that strong emission was

possible. Se fosse de origem

térmica, corresponderia a

Grote Reber's backyard radio telescope in Wheaton, IL. The parabolic reflector is about 10 m in diameter.

Only Grote Reber took Jansky's discovery

seriously. He was an amateur radio operator and professional radio engineer.

Em 1937 observou em 3300 MHz,

mas teve insucesso.

Grote Reber (22 dec 1911 – 20 dec 2002)

In 1938 he finally succeeded in

detecting and mapping (with about

10 degree angular resolution) the

Galaxy at 162 MHz, confirming

Jansky's discovery and

demonstrating that the radio

emission has a distinctly

nonthermal spectrum

http://www.cv.nrao.edu/course/astr534/Discovery.html

Henry Ford: o insucesso é apenas uma oportunidade

para recomeçar de novo

3300 MHz: nada

910 MHz: nada

Reber, G. 1940

(ApJ, 91, 621).

The radio sky

Céu em radio

(4.85 GHz) desde

Green Bank

Seen here is the radio sky over the

telescopes of the National Radio Astronomy Observatory in

Green Bank, VA. Note the shell-like

supernova remnants and irregularly shaped star formation regions. The point-like objects are not stars but

mostly distant radio galaxies.

htt p://w w w .c v. nra o.edu /c o urs e/ a s tr5 34 /T o ur .ht m l

The Sun at

4.6 GHz

http://metsahovi.aalto.fi/en/research/projects/solar_radio/mapping_tracking/

13.7m diameter radio telescope at Metsähovi, Kylmälä

Radio receiver for Planck CMB from Planck, an ESA mission

http://www.cea.inpe.br/roi/

Zonas de Silêncio

http://www.cea.inpe.br/roi/arquivos/ZonaSilencio_v2.pdf

Região de Atibaia. Ponto branco no meio é o observatório. O círculo maior é a zona de silêncio (R ~ 2 km). As elipses menores são regiões de desmatamento e degradação florestal. As maiores fontes de interferência são fornos de microondas, controles remotos, redes de alta tensão, walk talks, acionadores de lâmpadas

fluorescentes,

computadores e torres de celular.

http://www2.jpl.nasa.gov/magellan/

Venus by Magellan

(radar)

Animation of the variation of the synchrotron emission at 1400 MHz from Jupiter (VLA

observations) with a computer model (Levin et al. 2001, Geophys. Res. Lett., 28,903) using an assumed electron distribution and magnetic field. The model simulates ground based radio observations well. The thermal emission from Jupiter has been subtracted, and representative magnetic field lines are shown. The animation covers one rotation of Jupiter, frames are 20 degrees apart in central longitude. The animation shows the East West asymmetry of the emitted radiation in the equatorial plane. The "wobble" of the emitted radiation is due to the misalignment of the rotation pole of Jupiter and the magnetic pole.

h tt p :/ /ju n o .w isc .ed u /scie n ce_ma g n e tosphe re .html

http:// asd .gsfc. na sa.g ov/a rchi ve/a rcad e/scie nce _g al a xy .html

Mapa da galáxia em

408 MHz

The Galaxy in the 21cm line (1420.4 MHz) of neutral H. Red indicates directions of high HI column density, while blue and black show areas with little hydrogen

This false-color image of CO (J = 2-1) emission from the face-on spiral galaxy M51 was made with the Smithsonian Submillimeter Array (SMA). It reveals regions

containing dense molecular gas, dust, and star formation that are optically obscured.

Cassiopeia A (Cas A)

distance of about 11,000 light years from us. Its name is derived from the constellation in which it is seen:

Cassiopeia, the Queen. A radio supernova is the explosion that

occurs at the end of a massive star's life, and Cas A is the expanding shell of material that remains from such an explosion. This composite image is based on VLA data at three

different frequencies: 1.4, 5.0, and 8.4 GHz. The material that was ejected from the supernova

explosion can be seen in this image as bright filaments.

A high-resolution VLA image of the radio source Cygnus A. The bright central component is thought to coincide with a supermassive black hole that accelerates the relativistic electrons along two jets

terminating in lobes well outside the host galaxy.

The WMAP 7-year total-intensity image of the CMB. The intensity range is only 200uK

Pospelov & Pradler 2010 ARNPS 60, 539 Big Bang Nucleosynthesis as a Probe of New Physics

http://keckobservatory.org/news/international_team_on_keck_observatory_strengthens_big_bang_theory

Keck media release:

6/6/2013

“Back in 2004 HIRES was upgraded with CCDs having smaller pixels, allowing to see finer details in the spectrum,” University of Sao Paulo’s Jorge Meléndez said. “A high spectral resolution provided by HIRES is needed to study with exquisite detail the line profile and to estimate the presence of Lithium-6. The large light-collecting power of Keck Observatory allowed us to observe stars with a more ‘pristine’ composition than any previous study.”

SETI

Allen telescope array 350 dishes

(6m each)

Only 42 completed in 2007

(hibernation in April – Dec 2011 due

to lack of funds)

Wide field 2.45° at λ = 21 cm. Instantaneous frequency coverage from 0.5 to 11.2 GHz Arecibo

Resolução angular

⇨

Se λ = 0.1m e D = 7m,



_{= 1}

o

●

Rádiotelescópios são limitados pela difração

⇨

_{(lembrando...) os ópticos são limitados pelo seeing}



= 1.22

λ /d

λ (radio range observable from

Smith

No geral radiotelescópios não produzem imagens (detetores são

unidimensionais)

“Imageamento”

O rádio telescópio é um telescópio

com um “CCD” de um único pixel.

É necessário varrer a

região a ser observada.

Mas alguns rádio telescópios têm alimentadores múltiplos (Um CCD de mais de um pixel): O rádio telescópio de Parkes, 64 m, usa um receptor de 13 alimentadores em 21 cm, e o Five College

Radio Astronomy Observatory, 14 m, usa um receptor de 32 alimentadores no milimétrico!

Elementos de um radiotelescópio

Prato

+

Antena

+

sistema de

detecção

www.das.inpe.br

Prato: focaliza a radiação na antena

Rádiotelescópios não precisam ter superficies continuas

36

36

Rádiotelescópios tem f/# baixo

Baixa f/# ajuda a proteger do ruído

O rádio telescópio de Cambridge, com f/<1 e D=32m.

Podem ser off-focus (asimetricos,

e.g. seção de parábola)

• Green bank Radiotelescope, 100x110m (F=60m), largest

steerable in the world (situated in West Virginia, USA)

64-metre Parkes radio telescope in Australia.

The dish surface was physically upgraded by adding smooth metal plates to the central part to provide focusing capability for centimetre and millimetre length

Effelsberg 100-m Radio Telescope

Max Planck Institute for Radio Astronomy (Bonn)

- Located in a valley to minimize intereference - Accuracy of the mirror surface better than 1mm

Interferometria

BDA

10 antenas. 25 m cada.

Separação de 8600 km. 1,2-96 GHz.